1. The Field of the Invention
The present invention relates generally to a device for ankle rehabilitation or exercise.
2. The Background Art
The most common type of ankle injury is a sprain. A sprain is stretching and tearing of ligaments (fibrous bands connecting adjacent bones in a joint). Sprains may occur in any ligament in the ankle, but most sprains involve the lateral ligament complex, or the group of ligaments on the outside of the ankle. The ligaments are named for their location and the bones to which they are attached. The anterior talofibular ligament is on the front side. The posterior talofibular ligament is on the back side. And the calcaneofibular ligament is on the middle side. The most frequent sprain occurs when weight is applied to a foot which is on an uneven surface, and the foot rolls in. When the sole of the foot is pointing inward as force is applied, the ligaments stabilizing the lateral, or outside, part of the ankle are stressed. Thus, the sprains are caused by forced inversion and flexion movements of the ankle.
Ankle sprains are graded as 1, 2 or 3 depending on the extent of the injury. A grade 1 sprain is very mild and involves stretching of the ligaments, or small partial tears of the anterior talofibular ligament. A grade 2 sprain is a complete tear of the anterior talofibular ligament and the calcaneofibular ligament, but only mild stress to the posterior talofibular ligament. A grade 3 sprain involves a complete rupture of all the ligaments of the lateral complex. Complete restoration of muscle strength requires physical therapy and rehabilitation to avoid subsequent sprains. Residual weakness is common after any ankle sprain. Ankle stability may be improved over the long term by stretching and other exercises to strengthen leg and ankle muscles.
The ankle is a complex joint that is capable of moving in multiple planes. These multiple planes include: dorsi flexion, or bending the foot upwards; plantar flexion, or bending the foot downwards; inversion, or turning the foot so that the sole faces inward; eversion, or turning the foot so that the sole faces outward; internal rotation, or rotating the foot inwardly about an axis concentric with the lower leg; and external rotation, or rotating the foot outwardly about the axis. During rehabilitation it may be necessary to focus on a single, simple movement in an individual plane. Other exercises may require movement in multiple planes. For example, exercising the posterior tibialis muscle requires simultaneous movement in multiple planes, including plantar flexion, inversion and internal rotation.
Numerous devices have been developed to assist in exercising and rehabilitating ankle injuries. Many of these devices are overly simple, and fail to provide the necessary range of motion, or limit undesired motion to adequately support the ankle. For example, U.S. Pat. No. 5,722,919 discloses a weighted shoe-like device. Because the device relies on weight or gravity, the user must manipulate his/her body to properly orient the weight for the desired exercise. As another example, U.S. Pat. No. 4,337,939 has a foot platform pivotally coupled to a base. Because the device has a single pivot axis, motion is limited to a single plane.
Other devices are overly complex, bulky and expensive, and still fail to limit undesired motion or adequately support the ankle. For example, U.S. Pat. No. 4,452,447 discloses a foot platform coupled to a base through a gimble. Although the device allows movement in all planes, such movement is not limited to prevent re-injury. U.S. Pat. No. 4,605,220 discloses a foot platform coupled to a base through a universal joint and four shock absorbers. The device only allows movement in two planes and the foot platform cannot pivot. U.S. Pat. Nos. 4,186,920 and 5,368,536 disclose foot platforms coupled to a base through a ball joint. Again, although movement in all the planes is allowed, such movement is not limited.
Therefore, it would be advantageous to develop an ankle rehabilitation or exercise device capable of allowing proper movement of a user's ankle while avoiding re-injury. It would also be advantageous to develop such a device capable of resisting movement of the user's ankle in multiple planes of movement, but which is compact, portable, simple, and inexpensive. It would also be advantageous to develop such a device which limits or restricts movement of the user's ankle to a desired movement path.